Method and apparatus of growing silicon single crystal and silicon wafer fabricated thereby

ABSTRACT

Disclosed is a metod of fabrication of high quality silicon single crystal at high growth rate. The method grows silicon single crystal from silicon melt by Czochralski method, wherein the silicon single crystal is grown according to conditions that the silicon melt has an axial temperature gradient determined according to an equation, {(ΔTmax−ΔTmin)/ΔTmin}×100≦10, wherein ΔTmax is a maximum axial temperature gradient of the silicon melt and ΔTmin is a minimum axial temperature gradient of the silicon melt, when the axial temperature gradient is measured along an axis parallel to a radial direction of the silicon single crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of growing high qualitysilicon single crystal, and more particularly, to a method and apparatusof growing a high quality silicon single crystal ingot by controllingtemperature distribution of silicon melt during Czochralski growth ofsilicon single crystal, and silicone wafer fabricated thereby.

2. Description of the Related Art

As well known in the art, in order to grow a high quality silicon (Si)single crystal ingot that can enhance semiconductor device yield,temperature control has been conducted on high temperature distributionof the single crystal ingot mainly after crystallization. Thismethodology is intended to control stress that may be induced fromcontraction owing to cooling subsequent to crystallization or by thebehavior of point defects built up in solidification.

According to a typical process of Czochralski growth of Si singlecrystal, polycrystalline Si is loaded into a quartz crucible where it ismelted into Si melt under the heat radiated from a heater, and then a Sisingle crystal ingot is grown from the surface of Si melt.

When growing the Si single crystal ingot, the crucible is elevatedthrough the rotation of a shaft that supports the crucible, maintainingthe solid-liquid interface to a constant level, and the Si singlecrystal ingot is wound up as rotated coaxially with the crucible but inreverse direction.

Generally, for the purpose of efficient growth of the Si single crystalingot, inert gas such as argon Ar is blown into an ingot-growingapparatus via an upper portion thereof and exhausted from theingot-growing apparatus via a lower portion thereof.

Conventional techniques for growing a Si single crystal ingot as abovehave used a heat shield and a water cooling pipe in order to control thetemperature gradient of a growing Si single crystal. Examples of suchconventional techniques include Korean Patent No. 374703, Korean PatentNo. 0411571 and U.S. Pat. No. 6,527,859.

However, controlling the temperature gradient of single crystal is, byitself, not sufficient to manufacture a high quality Si single crystalingot and a Si wafer having low point defect concentration.

In particular, in case of fabricating semiconductor devices from a Siwafer manufactured according to a conventional technique, microprecipitates are formed from point defects through repeated heattreatment in device fabrication. As a drawback, the micro precipitatescause faults, resulting in poor device yield.

As disclosed in U.S. Pat. Nos. 5,919,302, 6,287,380 and 6,409,826, theaxial temperature distribution of crystal G₀ is in the form of G₀=c+ax²,making a tendency that vacancy concentration rises but interstitialconcentration descends from the periphery to the center of a wafer.Unless sufficient out-diffusion takes place in vicinity to the wafer,interstitial crystal defects such as LDP occur. Subsequently, it iscommon practice to conduct crystal growth with high vacancyconcentration in the center. Vacancy concentration, much higher thanequilibrium concentration, tends to create vacancy-related crystaldefects (e.g., void and Oxidation Induced Stacking Fault (OiSF)) in acentral portion of the wafer. Besides, even though a void or OiSF regionis controlled, micro precipitates may emerge from latent state throughseveral heat treatments in semiconductor fabrication.

Other conventional techniques, which control the temperaturedistribution of single crystal in order to manufacture a high quality Sisingle crystal, are as follows: Japanese Patent Application No. Hei02-119891 has been proposed to control the temperature distribution ofthe center and periphery of a Si single crystal ingot by adopting a hotzone during the cooling of the Si single crystal ingot in order toreduce lattice defects of the Si single crystal ingot owing to thestrain of solidification. With this technique, in particular, the use ofa cooling sleeve has enhanced solidification rate and reduced latticedefect in the growth direction of the Si single crystal ingot. JapanesePatent Application No. Hei 07-158458 has proposed to control thetemperature distribution and the pulling speed of a crystal ingot,whereas Japanese Patent Application No. Hei 07-66074 has proposed toimprove a hot zone and adjust cooling rate in order to control defectdensity. Japanese Patent Application No. Hei 04-17542 and U.S. Pat. No.6,287,380 have proposed to change a hot zone and control cooling rate inorder to restrict the formation of crystal defects by using thediffusion of point defects. Korean Patent Application No. 2002-0021524discloses that improvement in a heat shield and a cooling pipe hasenhanced the productivity of high quality single crystal. JapanesePatent Application Hei 05-61924 has proposed to periodically change thegrowth rate of crystal in order to utilize the hysteresis of a regionhaving crystal defects such as OiSF and oxygen precipitation defect,thereby preventing crystal defects in a Si single crystal ingot.

However, these conventional techniques are based upon solid statereaction, and thus have the following problems: First, there are anumber of hindrances to achieve an aim of high quality Si singlecrystal. For example, U.S. Pat. No. 6,287,380 is aimed to sufficientlydiffuse supersaturated point defects in a high temperature region beforegrowing them into crystal defects in order to drop point defectconcentration. However, temperature has to be maintained up to 16 hoursor more for this purpose, and thus this technique can be realized onlytheoretically but not in actual use.

Second, nearly all the conventional techniques have failed to have apractical effect. When a 200 mm diameter Si single crystal ingot wasgrown by periodically varying the pulling speed of the crystal ingot asproposed by Japanese Patent Application Hei 05-61924 and Eidenzon et al(Defect-free Silicon Crystals Grown by the Czochralski Technique,Inorganic Materials, Vol.33, No.3, 1997, pp.272-279), aimed high qualitywas not achieved but stability in process was incurred to the contrary.

Third, those inventions based upon solid state reaction cannot achievehigh productivity. Even though a heat shield and a water-cooling pipewere designed in optimal conditions according to the Korean PatentApplication No. 2001-7006403, this arrangement merely showed lowproductivity and pulling speed for high quality single crystal wasactually about 0.4 mm/min.

Another conventional technique for producing high quality Si singlecrystal is to control solid-liquid interface (crystal growth interface).Korean Patent Application No. 1998-026790 and U.S. Pat. No. 6,458,204limit the profile of a solid-liquid interface for producing high qualitySi single crystal. However, single crystal of sufficiently high qualitywas not produced in U.S. Pat. Nos. 5,919,302 and 6,287,380, even thoughthey have a solid-liquid interface proposed by the above inventions.

Moreover, the foregoing conventional techniques showed low productionyield in high quality single crystal.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and it is therefore an object of the present invention toprovide a method and apparatus for growing high quality Si singlecrystal in which point defect concentration is microscopicallycontrolled to such a degree that can eliminate faults in actualfabrication of devices.

It is another object of the invention to provide a method of growinghigh quality Si single crystal with high productivity.

It is further another object of the invention to provide a method ofgrowing high quality Si single crystal with high yield.

In order to realize the foregoing technical objects, the invention hasproposed to control the temperature distribution of Si melt during theCzochralski growth of Si single crystal in order to grow a high qualitySi crystal ingot by microscopically controlling the generation of pointdefects.

The invention provides a metod of growing a silicon single crystal fromsilicon melt by Czochralski method, wherein the silicon single crystalis grown according to conditions that the silicon melt has a temperaturegradient determined according to an equation,{(ΔTmax−ΔTmin)/ΔTmin}×100≦10, wherein ΔTmax is a maximum temperaturegradient of the silicon melt and ΔTmin is a minimum temperature gradientof the silicon melt, when the temperature gradient is measured along anaxis parallel to a radial direction of the silicon single crystal nearthe solid-liquid interface.

Preferably, the silicon single crystal is grown satisfying the aboveequation as well as following conditions that when the temperature ofthe silicon melt is measured along an axis parallel to a longitudinaldirection of the silicon single crystal, the silicon single crystal isgrown according to conditions that the temperature of the silicon meltmeasured starting with the solid-liquid interface rises gradually up toa hottest point and then descends gradually as getting away from thesilicon single crystal, and the rising temperature gradient of the meltis kept larger than the descending temperature gradient of the melt.

Preferably, the axis is a central axis passing through the center of thesilicon single crystal.

Preferably, the temperature gradient of the silicon melt measured alongthe axis parallel to the radial direction of the single crystal is takena portion of the silicon melt ranging from the interface to the hottestpoint.

Preferably, the axis parallel to the longitudinal direction of thesingle crystal passes through the center of the silicon single crystal.

The hottest point may be positioned in a portion of the silicon meltcorresponding to ⅕ to ⅔ of the total depth of the silicon melt from thesurface, and preferably in a portion of the silicon melt correspondingto ⅓ to ½ of the total depth of the silicon melt from the surface.

The invention provides a method of growing silicon single crystal fromsilicon melt by Czochralski method, wherein the silicon single crystalis grown according to equation: 3≦Ln[Vs/Vc]≦5, wherein Vc is a rotationspeed of a crucible containing the silicon melt, and Vs is the rotationspeed of the silicon single crystal.

It is preferable that the silicon single crystal is grown from thesilicon melt under magnetic field. More preferably, the magnetic fieldis applied to the silicon melt in a direction vertical or horizontal tothe longitudinal direction of the single crystal, or in CUSP type.

Also, a heater may be provided at sides of the silicon melt to heat thesilicon melt so that heat generation in a portion of the silicon meltcorresponding to ⅕ to ⅔ of the total depth of the silicon melt from thesurface is increased over surrounding portions of the silicon melt.

The magnetic field can promote heat flow directed from a portion mostadjacent to the heater toward the center of the solid-liquid interfaceor a high temperature region of the melt.

The invention also provides an apparatus for growing silicon singlecrystal from silicon melt by Czochralski method, the apparatusincluding: a chamber; a crucible provided inside the chamber, andcontaining silicon melt; a heater provided at sides of the crucible toheat the silicon melt so that heat generation in a portion of thesilicon melt corresponding to ⅕ to ⅔ of the total depth of the siliconmelt from the surface is increased over surrounding portions of thesilicon melt; and a magnet provided at sides of the crucible to applymagnetic field to the silicon melt The apparatus of the invention mayfurther include a heat shield provided between the silicon singlecrystal and the crucible, surrounding the silicon single crystal, inorder to shield heat dissipation from the silicon single crystal; and aheat cover provided in the heat shield in a portion most adjacent to thesilicon single crystal, surrounding the silicon single crystal.

The silicon wafer manufactured by the foregoing apparatus and method haspoint defect concentration that is the same as or less than criticalsaturation concentration of vacancies that is a minimum vacancyconcentration allowing the formation of micro precipitates in heattreatment.

It is preferable that the heat treatment includes first heat treatmentat 700 to 800° C. for 5 to 7 hours and second heat treatment at 1000 to1100° C. for 14 to 18 hours. Preferably, the micro precipitates areformed inside the wafer at least 1 μm deep from the surface of thewafer, and sized 0.3 μm or less.

The invention also provides a silicon single crystal ingot grown by theforegoing apparatus and method and a silicon wafer obtained from theingot have point defect concentration of 10¹⁰˜10¹²/cm³.

In the silicon single crystal ingot or wafer, it is preferable that aninterstitial dominant region is a central portion and a vacancy dominantregion is in a periphery.

Preferably, the point defect concentration is uniform so that adifference between a maximum point defect concentration (Cmax) and aminimum point defect concentration (Cmin) is 10% or less of the minimumpoint defect concentration (Cmin) in a region up to 90% or less of thediameter of the silicon single crystal ingot or wafer from the center.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view illustrating a process of Si single crystalgrowth by Czochralski method according to an embodiment of theinvention, with the axial temperature gradient profile of Si meltmeasured along an axis in parallel to the radial direction of a singlecrystal ingot;

FIG. 2 is a sectional view illustrating a process of Si single crystalgrowth by Czochralski method according to an embodiment of theinvention, with the temperature profile of Si melt measured along thelongitudinal direction of a single crystal ingot;

FIG. 3 is a graph showing the temperature difference of the melt ΔTrtaken from the center toward the wall of the crucible in the radialdirection, at ⅕ depth point of the Si melt;

FIG. 4 is a graph showing the growth rate of the high quality siliconsingle crystal ingot with respect to log value Ln[Vs/Vc] obtained by therotation speed of the crucible and the rotation speed Vs of the siliconsingle crystal ingot;

FIG. 5 is a schematic view illustrating a process of Si single crystalgrowth under magnetic field according to the invention;

FIG. 6 is a valuation result of crystal defect of silicon single crystalingot grown by Comparative Example 3;

FIGS. 7 a and 7 b are graphs illustrating the relation between thegrowth rate for high quality Si single crystal and the temperaturedifference of Si single crystal, with respect to Examples 1 to 3 andComparative Examples 1 to 3; and

FIGS. 8 a to 8 d are graphs illustrating the relation between the growthrate for high quality Si single crystal and the temperature differenceof Si melt, with respect to Examples 1 to 3 and Comparative Examples 1to 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription and drawings, the same reference numerals are used todesignate the same or similar components, and so repetition of thedescription on the same or similar components will be omitted.

The present invention starts from the conception that in growing solidSi single crystal from Si melt, the growth of a high quality Si singlecrystal ingot with minimized point defect is not obtained from merelycontrolling single crystal temperature gradient and solid-liquidinterface profile, and is made based upon the fact that there exists amore decisive factor for the growth of a high quality Si single crystal.

In order to overcome restrictions in solid state reaction occurring insubsequent to crystallization, liquid state prior to solidification hasbeen analyzed thoroughly, and as a result, it was found that thetemperature distribution of Si melt is very important.

Crystal growth is generally carried out as growth units such as atoms ormolecules migrate to a crystal growth interface or metastable region andthe adhere to the interface, in which rising temperature gradient in Simelt increases driving force of the growth units in liquid state tendingto migrate to the crystal growth interface or metastable region.

Herein the crystal growth interface is also referred to ascrystallization interface or solid-liquid interface(or crystal-meltinterface) where a solid Si single crystal ingot meets liquid Si melt.The metasable region refers to a status of liquid Si melt ready forsolidification, which has incomplete crystallinity.

Since high temperature gradient in Si melt enhances growth units toparticipate in crystal growth, relatively low crystal-pulling speedcauses excessive atoms to crystallize, thereby impartingself-interstitial rich characteristics to a Si single crystal ingot. Onthe contrary, relatively low temperature gradient in Si melt cannotprovide a sufficient number of atoms to be crystallized, so that highcrystal-pulling speed makes the Si single crystal ingot have a vacancyrich characteristic.

FIG. 1 is a schematic view illustrating a process of Si single crystalgrowth by Czochralski method according to an embodiment of theinvention. As shown in FIG. 1, an apparatus for manufacturing a Sisingle crystal ingot according to the invention includes a chamber 10where the Si single crystal ingot is grown.

A quartz crucible 20 containing Si melt SM is installed inside thechamber 10, and a crucible support 25 made of graphite is installedsurrounding the quartz crucible 20.

The crucible support 25 is fixed on a rotary shaft 30, which is rotatedby drive means (not shown) to turn and elevate the quartz crucible 20,thereby maintaining a solid-liquid interface to a predetermined level.The crucible support 25 is surrounded by a cylindrical heater 40 at apredetermined gap, and the heater 40 is surrounded by a barrel-shapedthermostat or heat insulator 45.

That is to say, the heater 40 is installed aside the quartz crucible 20to heat high purity polycrystal Si lump loaded in the quartz crucible 20into Si melt SM, and the heat insulator 45 prevents heat radiated fromthe heater 40 from dispersing toward the wall of the chamber 10 therebyto enhance heat efficiency.

Pulling means (not shown) is installed above the chamber 10 to wind up acable, and a seed crystal is installed at a bottom of the cable incontact with the Si melt SM inside the quartz crucible 20 so that a Sisingle crystal ingot IG is grown by elevating the seed crystal throughwinding-up of the cable. The Pulling means carries out rotation whilewinding up the cable during the growth of the Si single crystal ingotIG, in which the Si single crystal ingot IG is raised while beingrotated coaxially with the rotary shaft 30 of the crucible 20 but inreverse direction.

Inert gases such as Ar, Ne and N are supplied to the growing singlecrystal ingot IG and the Si melt SM via a top portion of the chamber 10,and used inert gas is exhausted out via a lower portion of the chamber10.

A heat shield 50 is installed between the Si single crystal ingot IG andthe crucible 20 to surround the ingot IG in order to prevent heatdissipation from the ingot IG. A cylindrical heat cover 46 is alsoattached to the heat shield 50 at a portion most adjacent to the Sisingle crystal ingot IG in order to further shield heat flow, therebykeeping heat.

The present invention is aimed to control the temperature of the Si meltSM to be uniform in the radial direction of the Si single crystal ingotIG.

In order to provide more detailed explanation, FIG. 1 shows isothermallines marked in the Si melt SM together with a axial temperaturegradient profile of the Si melt SM measured along an imaginary axisparallel to the radial direction of the Si single crystal ingot IG.

Examining the temperature of the Si melt SM in general, a highest melttemperature (designated with T_(P) region in FIG. 1) is found in alateral portion of the crucible most adjacent to the heater 40 as a heatsource, and a lowest melt temperature is found as solidificationtemperature in a solid-liquid interface where crystal growth takesplace.

In measurement of the temperature gradient of the Si melt SM along theaxis parallel to the radial direction of the Si single crystal ingot IG,the temperature gradient is a vertical instantaneous gradient, which ispreferably measured at the Si melt located under the Si single crystalingot IG.

When the measured temperature gradient has a maximum ΔTmax and a minimumΔTmin, the Si single crystal ingot IG is grown in conditions accordingto Equation (1) below:{(ΔTmax−ΔTmin)/ΔTmin}×100≦10   (1)

Equation (1) implies that temperature is controlled so that thedifference between the maximum temperature gradient ΔTmax and theminimum temperature gradient ΔTmin is 10% or less of the minimumtemperature gradient ΔTmin. The temperature difference is preferably 5%or less, more preferably 3% or less, and further more preferably 1% orless.

If the temperature of the Si melt SM becomes ununiform in the radialdirection of the Si single crystal ingot IG in such a degree that thedifference between the maximum temperature gradient ΔTmax and theminimum temperature gradient ΔTmin exceeds 10% of the minimumtemperature gradient ΔTmin, it is impossible to obtain high quality Sisingle crystal proposed by the invention. Since the temperature of theSi melt can be varied periodically under the influence of meltconvection, mean value is preferably taken as the measured temperature.

The invention also proposes the existence of a high temperature region(marked with T_(H) in FIG. 1) relatively hotter than surrounding regionswithin the melt, and particularly, to control the temperature gradientat top and bottom portions of the high temperature region T_(H).

In order to give a more detailed description, FIG. 2 shows a temperatureprofile of the Si melt measured along an axis X parallel to thelongitudinal direction of the single crystal ingot.

When measuring the temperature of the Si melt SM along the axis parallelto the longitudinal direction of the single crystal ingot IG, thetemperature of the Si melt SM measured starting with the solid-liquidinterface rises gradually up to a hottest point H as getting away fromthe single crystal ingot IG and then descends gradually as getting awayfrom the hottest point H toward the bottom of the Si melt SM, which ismost remote from the single crystal ingot IG.

Preferably, the Si single crystal ingot IG is grown by maintaining acondition ΔTi>ΔTd, in which ΔTi is melt temperature gradient rising fromthe solid-liquid interface up to the hottest point H, and ΔTd is melttemperature gradient descending from the hottest point H to the meltbottom. The axis X as a reference of indicating temperature measurementposition is preferably a central axis passing through the center of theSi single crystal ingot IG.

The hottest point H preferably exists at a point of about ⅕ to ⅔ of thetotal depth of the Si melt SM from the surface, and more preferably at apoint of about ⅓ to ½ of the total depth of the Si melt SM.

More preferably, the single crystal ingot is grown by meeting Equation(1) above while keeping the condition ΔTi>ΔTd.

In case of measuring the temperature gradient of the Si melt mentionedin Equation (1) above along the axis parallel to the radial direction ofthe single crystal ingot, the temperature gradient of the Si melt ispreferably measured at a melt region from the solid-liquid interfacewhere crystal growth takes place to the level D₁ of the hottest point H.

The temperature gradient profile shown in FIG. 1 is measured at a point⅕ deep from the surface of the Si melt SM.

In the invention, it was also found that the temperature distribution ofthe Si melt SM in the radial direction of single crystal is associatedwith the rotation speed of the crucible 20 containing the Si melt SM.Rotating the crucible containing the Si melt gives centrifugal force tothe Si melt, in which centrifugal force F applied to the Si melt perunit volume is expressed as F=mrω², in which m is the mass of Si meltunit volume, r is the distance from the center axis, and ω is angularvelocity applied to the Si melt per unit volume. The angular velocity ωmay also be referred to as the rotation speed of the crucible. Otherfactors such as frictional force will not be considered owing torelatively low viscosity of the Si melt.

The centrifugal force F applied to the Si melt per unit volume increaseslinearly as Si melt position changes from the center of the singlecrystal ingot radially toward the periphery, and in proportion to thesquare of the rotation speed of the crucible.

FIG. 3 is a graph showing the temperature difference of the melt ΔTrtaken from the center toward the wall of the crucible in the radialdirection, at ⅕ depth point of the Si melt (from the surface).

It is apparent that the temperature difference of the melt ΔTr decreasesaccording to a decrease in rotation speed of the crucible, that is,descending from curve ω₃ to curve ω₁, such that the temperaturedistribution of the melt becomes uniform in the radial direction.

As a result, in order to make the temperature of the Si melt uniform inthe radial direction of single crystal, the rotation speed should dropas low as possible, for example, to 2 rpm or less, preferably to 1 rpmor less, and more preferably 0.6 rpm or less.

Furthermore, in order to manufacture high quality single crystal at highproductivity, it is required to determine the operational range of therotation speed of the single crystal ingot IG according to the rotationspeed of the crucible 20. FIG. 4 is a graph showing the growth rate ofthe Si single crystal ingot with respect to log value Ln[Vs/Vc] obtainedby the rotation speed of the crucible Vc and the rotation speed of thesilicon single crystal ingot Vs. In the graph shown in FIG. 4, Vpindicates the growth rate of high quality single crystal according tothe invention, and Vo indicates the growth rate of the prior art.

A tendency can be confirmed from the graph shown in FIG. 4 where thegrowth rate of high quality single crystal rises up to a predeterminedrange but descends past the predetermined range according to risingLn[Vs/Vc] value. This originates from the fact as disclosed in KoreanPatent Application No. 2003-0080998 that was previously filed by theinventor. That is, when single crystal rotates too fast compared to slowrotation of the crucible, cold melt rises up from the bottom of thecrucible, thereby cooling the high temperature region, and thus droppingthe axial temperature gradient of the melt. In addition, abnormal growthof crystal may take place if the temperature gradient of the meltbecomes excessively small in the radial direction of single crystal invicinity of triple point where single crystal (solid), melt (liquid) andatmosphere (gas) meet together. So, it is preferably to avoid such avalue in case of setting Ln[Vs/Vc] value. Through these results, theinvention has been made to grow Si single crystal under conditionsaccording to Equation (2) below:3≦Ln[Vs/Vc]≦5   (2),where Vc is the rotation speed of the crucible, and Vs is the rotationspeed of single crystal.

As an alternative, the invention can make the temperature of the Si meltmore uniform in the radial direction of single crystal by using magneticfield. That is, Si single crystal is grown from the Si melt under themagnetic field. Magnetic field may be applied to the Si melt verticallyor horizontally to the longitudinal direction of single crystal, or CUSPmagnetic field may be applied to the Si melt.

FIG. 5 is a schematic view illustrating a process of growing Si singlecrystal under CUSP magnetic field, in which profiles of magnetic forcelines are shown. Magnetic field controls the convention of the Si melt,and more particularly, restricts the flow of the Si melt in directionperpendicular to the magnetic force lines, thereby influencing heatflow. Accordingly, magnetic field applied to the Si melt promotes heatflow directed from the hottest region T_(P) most adjacent to the heatertoward the center of the solid-liquid interface or a hot region T_(H) ofthe Si melt.

Since the magnetic field assists heat conduction from the hottest regionT_(P) to the hot region T_(H), the temperature gradient of the melt onthe rise or the temperature difference between the solid-liquidinterface and the hot region T_(H) becomes larger, thereby increasingthe growth rate of high quality crystal.

In addition, the invention can improve the heater in order to producethe position of the hottest point H and the temperature gradient in theSi melt SM according to preset conditions. For example, the Si singlecrystal ingot can be grown by increasing heat generation from the heater40 installed around the Si melt at portions corresponding to ⅕ to ⅔ ofthe total depth from the surface of the Si melt.

More preferably, heat generation from the heater 40 can be increased atportions corresponding to ⅓ to ½ of the total depth from the surface ofthe Si melt over surrounding portions.

For example, a heater using Joule's heat produced from current flowingthrough resistance wire can increase resistance in portionscorresponding to ⅕ to ⅔, and more preferably, in portions correspondingto ⅓ to ½ of the total depth from the surface of the Si melt. Theresistance of specific portions in the heater can be increased basedupon a fact that resistance is proportional to specific resistance andlength but inverse proportional to cross section, for example, byreducing the cross section of the resistance wire or using a heatermaterial of high specific resistance.

Example 1 used an apparatus for growing Si single crystal as shown inFIG. 1, and increased the resistance of a heater portion correspondingto ⅕ depth from the melt surface.

The temperature of the Si single crystal ingot and the Si melt wasmeasure with a thermocouple, and its results are reported in Tables 1and 2 below.

After measuring the temperature difference between the solid-liquidinterface and a single crystal point distanced 50 mm from thesolid-liquid interface (expressed with crystal ΔT(50 mm)=1410°C.−T_(50 mm)), obtained by subtracting T_(50 mm) at the single crystalpoint distanced 50 mm from solid-liquid interface temperature 1410° C.and the temperature difference between the solid-liquid interface and asingle crystal point distanced 100 mm from the solid-liquid interface(expressed with crystal ΔT(100 mm)=1410° C.−T_(100 mm)), their resultsare reported in Table 1, expressed in ratios with respect to referencevalues.

Table 2 reports measurement results of the temperature difference AT ofthe Si melt in depth, in which the temperature difference between thesolid-liquid interface temperature 1410° C. and melt temperature atseveral points corresponding to ⅕, ¼, ⅓, ½, ⅔, ¾ and ⅘ of the totaldepth of the Si melt from the surface were measured, and expressed inratios with respect to reference values. For example, “melt ΔT (⅕depth)” indicates a value produced by subtracting melt temperature at ⅕depth point with respect to the total depth of the Si melt from 1410°C., and expressed with a ratio about reference value LT⅕.

The results of Examples 1 to 3 and Comparative Examples 1 to 3 as shownin Tables 1 and 2 are values expressed in ratios with respect toreference values. The reference values indicate a temperature profile inwhich the temperature of the Si melt rises gradually as approaching thebottom of the crucible away from the solid-liquid interface but thegradient of rising temperature becomes smaller gradually. TABLE 1 GrowthCondition Crystal ΔT (50 mm) Crystal ΔT (100 mm) Reference ST50 ST100Exam. 1 1.99 1.94 Exam. 2 2.00 1.96 Exam. 3 2.02 1.97 Comp. Exam. 1 1.961.92 Comp. Exam. 2 2.08 2.04 Comp. Exam. 3 2.10 2.09

TABLE 2 Melt ΔT (at points with respect to depth) High Quality GrowthCondition ⅕ ¼ ⅓ ½ ⅔ ¾ ⅘ Growth Rate (V) Reference LT1/5 LT1/4 LT1/3LT1/2 LT2/3 LT3/4 LT4/5 V0 Exam. 1 1.31 1.31 1.31 1.30 1.10 1.00 0.921.31 Exam. 2 1.30 1.31 1.31 1.30 1.13 1.05 0.96 1.31 Exam. 3 1.30 1.301.31 1.31 1.15 1.08 0.99 1.31 Comp. Exam. 1 1.09 1.08 1.08 1.08 1.091.10 1.10 1.09 Comp. Exam. 2 1.10 1.09 1.10 1.10 1.13 1.15 1.15 1.09Comp. Exam. 3 1.09 1.08 1.08 1.08 1.09 1.10 1.10 1.09

As shown in Table 2 above, in Example 1, the temperature of the Si meltrose gradually reaching about 1.3 times over the reference value at ⅕depth point from the surface in a direction away from the solid-liquidinterface, and reached the highest point after passing ½ depth pointfrom the surface. The Si melt temperature descended gradually from thehighest point meeting a point between ¾ depth and ⅘ depth—which has thesame temperature as the reference value—and past this point, droppedunder the reference value. In this case, rising temperature gradient waslarger than descending temperature gradient, and Si single crystal wasgrown under the melt temperature conditions as mentioned above.

Example 2 used a growing apparatus the same as that of Example 1, withraised resistance of a heater portion corresponding to ⅓ depth pointfrom the surface of the melt. The temperatures of a single crystal ingotand melt were measured, and their results are reported in Table 2 above.

Example 3 used a growing apparatus the same as that of Example 1, withraised resistance of a heater portion corresponding to ⅔ depth pointfrom the surface of the melt The temperatures of a single crystal ingotand melt were measured, and their results are reported in Table 2 above.

In Comparative Example 1, a Si single crystal ingot was grown accordingto a conventional technique that controls the temperature distributionof the ingot. The temperatures of the Si single crystal ingot and meltwere measured, and their results are reported in Table 2 above.

In Comparative Example 2, a single crystal ingot was grown according toa conventional technique that applies strong horizontal magnetic fieldto control the solid-liquid interface profile of crystal growth to beconvex toward the single crystal ingot as disclosed by Korean PatentApplication No. 1998-026790. The temperatures of the single crystalingot and melt were measured, and their results are reported in Table 2above.

In Comparative Example 3, a 200 mm diameter Si single crystal ingot wasgrown according to a conventional technique that periodically changesthe pulling speed of the crystal ingot as disclosed by Japanese PatentApplication Hei 05-61924. The temperatures of the single crystal ingotand melt were measured, and their results are reported in Table 2 above.

In addition, crystal defect evaluation results of the Si single crystalingot grown according to Comparative Example 3 are shown in FIG. 6. InComparative Example 3, the pulling speed was changed at a period of 30to 60 minutes, and the fluctuation of the pulling speed was 2 to 3 timesof the smallest pulling speed. Despite of such periodic change in thepulling speed, quality result in FIG. 2 shows that the growth rate ofhigh quality single crystal was not improved and high quality was notfully obtained in the radial direction of the ingot with vacancydominant defects. Even though conventional techniques can be realized,the diameter of a Si single crystal ingot is limited within about 80 mm.In the case of a Si single crystal ingot diameter of 200 mm as inComparative Example 3, it was impossible to manufacture high quality Sisingle crystal from solid state diffusion.

As reported in Table 2 above, the temperatures of the Si melt inComparative Examples 1 to 3 do not comply with conditions proposed bythe invention. The temperature of the melt in Comparative Examples 1 to3 rose continuously in a direction away from the solid-liquid interfaceuntil reaching the bottom of the crucible.

When quality evaluation was made on a single crystal ingot after thecompletion of single crystal growth, Examples 1 to 3 showed 20%improvement over Comparative Example 1 in high quality single crystalgrowth rate.

FIGS. 7 a and 7b and FIGS. 8 a to 8 d are graphs illustrating therelation of growth rate V/VO with temperature difference.

FIGS. 7 a and 7 b and FIGS. 8 a to 8 d are graphs illustrating therelation between the growth rate V/VO for high quality Si single crystaland the temperature difference.

FIG. 7 a shows single crystal temperature difference ΔT_(s50)/ΔT0between solid-liquid interface and 50 mm point, and FIG. 7 b showssingle crystal temperature difference T_(s100)/ΔT0 between solid-liquidinterface and 100 mm.

FIG. 8 a shows temperature difference ΔT₁₅/ΔT0 between the solid-liquidinterface and ⅕ depth point from the surface with respect to the totaldepth of the Si melt, and FIG. 8 b shows temperature difference ΔT₁₄/ΔT0between the solid-liquid interface and ¼ depth point from the surfacewith respect to the total depth of the Si melt. FIG. 7 c showstemperature difference ΔT₁₃/ΔT0 between the solid-liquid interface and ⅓depth point from the surface with respect to the total depth of the Simelt, and FIG. 8 d shows temperature difference ΔT₁₂/ΔT0 between thesolid-liquid interface and ½ depth point from the surface with respectto the total depth of the Si melt.

In FIGS. 7 a and 7 b, V/G is not constant, and thus it was found thatthe growth rate of high quality single crystal is not directlycorrelated with the temperature difference of crystal.

On the contrary, in FIGS. 8 a to 8 d, the growth rate of high qualitysingle crystal showed considerable correlation with the temperaturegradient of the melt, in which the growth rate divided by thetemperature gradient of the melt made a constant value. So, it was foundthat the temperature gradient of the melt was a decisive factor forgrowing high quality single crystal, and the growth rates in highquality single crystal in Examples 1 to 3 were improved over ComparativeExamples 1 to 3.

By optimizing the temperature distribution of the melt as describedabove, it was found that high quality single crystal free of crystaldefects was obtained easily and growth rate was improved remarkably.

This phenomenon results from the fact that when rising temperaturegradient of the melt from the solid-liquid interface to the highestpoint is made larger, driving force for moving growth units such asatoms and molecules toward crystal growth interface is increased. Thisas a result can accelerate the pulling speed of crystal or the growthrate of high quality crystal that minimizes point defects such asvacancy and interstitial.

Through heater improvement, magnetic field application and controlledrotation speed of crucible and single crystal as mentioned above, thetemperature distribution of the Si melt in single crystal radiusdirection and single crystal length direction is optimized as describedabove owing to so-called “channel effect.”

Channel effect refers to minimum-loss heat flow from a hottest regiontoward a high temperature region of the melt along an imaginary channel100 as shown in FIG. 4. Such channel effect can increase the risingtemperature gradient of the melt, that is, the temperature gradient ofthe melt from the solid-liquid interface to a high temperature region.Besides, the crucible bottom becomes relatively cold thereby restrictingoxygen dissolution therefrom.

With the above described means, the invention can control point defectssuch as vacancy and interstitial, thereby restricting various defectssuch as dislocation as growth defect (e.g., edge, screw and loop typedislocations), stacking fault and void as a group of vacancies.

As a result, a Si single crystal ingot grown by the apparatus and methodas described above has a low point defect concentration of10¹⁰˜10¹²/cm³. This point defect concentration corresponds to criticalvacancy saturation concentration as a minimum vacancy concentration thatcan form micro precipitates in an active area of a device during heattreatment in the fabrication of devices from a wafer obtained from theingot.

Current development in wafer manufacturing technique has achieveddefect-free wafer level in as-grown state from low point defectconcentration of 10¹¹ to 10¹³/cm³. However, even a defect-free as-grownwafer having point defect concentration of 10¹¹ to 10¹³/cm³ createssecond defects such as micro precipitates in an active area of a deviceowing to heat treatment during actual device fabrication from the wafer.

In this way, the invention provides wafers having lower point defectconcentration in order to prevent such second defects. The invention canimpart high productivity to wafers having point defect concentration ata level the same as or less than critical vacancy saturationconcentration that is a minimum vacancy concentration by which microprecipitates can be formed in a device active area during heattreatment.

In this case, heat treatment conditions functioning as reference fordefining critical vacancy saturation concentration include first heattreatment carried out at 700 to 800° C. for 5 to 7 hours and second heattreatment carried out at 1000 to 1100° C. for 14 to 18 hours. Inaddition, micro precipitates are sized 0.3 μm or less, and formed insidethe wafer at least 1 μm deep from the surface of the wafer.

A wafer of the invention having point defect concentration of 10¹⁰ to10¹²/cm³ as mentioned above does not create secondary defects such asmicro precipitates even after undergoing any types of device fabricationprocesses.

In the past, a central portion of a wafer has been a vacancy dominantregion and its periphery was an interstitial dominant region. However,the distribution is currently getting reversed owing to the developmentof wafer fabrication techniques. Accordingly, also in the presentinvention, an interstitial dominant region may be formed in a centralportion of a Si ingot and a wafer, and a vacancy dominant region may beformed in the periphery. Moreover, even a balanced region is obtained inwhich interstitial concentration is balanced with vacancy concentrationwithout any interstitial dominant region or vacancy dominant region.

Furthermore, since the invention is based upon fluid mechanism ofenhanced turbulent flow, an interstitial dominant region and a vacancydominant region are found substantially asymmetric about a central axisin the longitudinal direction of an ingot. However, this does not causeany problem in obtaining a high quality single crystal ingot and wafer.That is, in a silicon wafer manufactured according to the invention, theinterstitial dominant region and the vacancy dominant region arearranged substantially asymmetric about the center of the wafer. Radialprofiles of point defect concentrations are also substantiallyasymmetric about the center of the wafer.

Furthermore, a Si single crystal ingot and a wafer manufacturedaccording to the invention have uniform point defect distribution. Forexample, in case of measuring point defect concentration in a regionwithin 90% of the radius from the center of the ingot or wafer, thedifference between the maximum point defect concentration Cmax and theminimum point defect concentration Cmin is 10% or less of the minimumpoint defect concentration Cmin. That is, point defects are distributeduniform satisfying a condition (Cmax−Cmin)/Cmin×100≦10(%).

Generally two types of convection exist in the melt. That is, theconvection distribution of the melt SM is divided into an outsideportion that rises to the surface of the melt SM along the bottom andsidewall of the crucible and then circulates to the single crystal ingotalong the surface of the melt SM and an inside portion that circulatesadjacent to the bottom of the single crystal ingot along the insideinclination of the periphery.

Examples of melt convention preferable in the invention are described indetail in Korean Patent Application No. 2003-0080998, by which thequality of single crystal can be made more uniform in its radialdirection.

As described above, the invention can control the temperaturedistribution of the Si melt according to specific conditions proposed bythe invention in order to grow a high quality Si single crystal ingot,and owing to high growth rate, achieve high productivity.

Furthermore, the invention has an advantageous effect of providing ahigh quality Si single crystal ingot and a Si wafer having a low pointdefect concentration to a level that can prevent secondary defects suchas micro precipitates through heat treatments in actual devicefabrication.

Using a wafer cut from such a high quality single crystal ingot canenhance the yield of electronic devices.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A method of growing a silicon single crystal from silicon melt byCzochralski method, wherein the silicon single crystal is grownaccording to conditions that the silicon melt has an axial temperaturegradient determined according to an equation,{(ΔTmax−ΔTmin)/ΔTmin}×100<10, wherein ΔTmax is a maximum axialtemperature gradient of the silicon melt and ΔTmin is a minimum axialtemperature gradient of the silicon melt, when the temperature gradientis measured along an axis parallel to a radial direction of the siliconsingle crystal.
 2. The method according to claim 1, wherein the axialtemperature gradient is a mean axial temperature gradient.
 3. The methodaccording to claim 1, wherein the axis is a central axis passing throughthe center of the silicon single crystal.
 4. The method according toclaim 1, wherein, when the temperature of the silicon melt is measuredalong an axis parallel to a longitudinal direction of the silicon singlecrystal, the silicon single crystal is grown according to conditionsthat the temperature of the silicon melt measured starting with aninterface between the silicon melt and the single crystal risesgradually up to a hottest point and then descends gradually as gettingaway from the silicon single crystal, and the rising temperaturegradient of the melt is kept larger than the descending temperaturegradient of the melt.
 5. The method according to claim 4, wherein thetemperature gradient of the silicon melt measured along the axisparallel to the radial direction of the single crystal is taken aportion of the silicon melt ranging from the interface to the hottestpoint.
 6. The method according to claim 1, wherein the temperaturegradient of the silicon melt measured along the axis parallel to theradial direction of the single crystal is taken from a portion of themelt positioned under the single crystal.
 7. The method according toclaim 4, wherein the axis parallel to the longitudinal direction of thesingle crystal passes through the center of the silicon single crystal.8. The method according to claim 4, wherein the hottest point ispositioned in a portion of the silicon melt corresponding to ⅕ to ⅔ ofthe total depth of the silicon melt from the surface.
 9. The methodaccording to claim 8, wherein the hottest point is positioned in aportion of the silicon melt corresponding to ⅓ to ½ of the total depthof the silicon melt from the surface.
 10. A method of growing siliconsingle crystal from silicon melt by Czochralski method, wherein thesilicon single crystal is grown according to an equation:3≦Ln[Vs/Vc]≦5, wherein Vc is a rotation speed of a crucible containingthe silicon melt, and Vs is the rotation speed of the silicon singlecrystal.
 11. The method according to claim 1, wherein the silicon singlecrystal is grown according to an equation:3≦Ln[Vs/Vc]≦5, wherein Vc is a rotation speed of a crucible containingthe silicon melt, and Vs is the rotation speed of the silicon singlecrystal.
 12. The method according to claim 1, wherein the silicon singlecrystal is grown from the silicon melt under magnetic field.
 13. Themethod according to claim 12, wherein the magnetic field is applied tothe silicon melt in a direction vertical or horizontal to thelongitudinal direction of the single crystal, or in CUSP type.
 14. Themethod according to claim 1, wherein a heater is provided at sides ofthe silicon melt to heat the silicon melt so that heat generation in aportion of the silicon melt corresponding to ⅕ to ⅔ of the total depthof the silicon melt from the surface is increased over surroundingportions of the silicon melt.
 15. The method according to claim 12,wherein a heater is provided at sides of the silicon melt to heat thesilicon melt so that heat generation in a portion of the silicon meltcorresponding to ⅕ to ⅔ of the total depth of the silicon melt from thesurface is increased over surrounding portions of the silicon melt. 16.A silicon wafer manufacturing method of wafer-processing a siliconsingle crystal ingot grown according to claim 1 into high qualitywafers.
 17. An apparatus for growing silicon single crystal from siliconmelt by Czochralski method, comprising: a chamber; a crucible providedinside the chamber, and containing silicon melt; a heater provided atsides of the crucible to heat the silicon melt so that heat generationin a portion of the silicon melt corresponding to ⅕ to ⅔ of the totaldepth of the silicon melt from the surface is increased over surroundingportions of the silicon melt.
 18. The apparatus according to claim 17,further comprising a magnet provided at sides of the crucible to applymagnetic field to the silicon melt.
 19. The apparatus according to claim18, wherein the magnet is adapted to apply magnetic field that promotesmelt convection from a portion of the melt most adjacent to the heatertoward the center of the single crystal.
 20. The apparatus according toclaim 17, wherein the heater is adapted to increase heat generation in aportion of the silicon melt corresponding to ⅓ to ½ of the total depthof the silicon melt from the surface over surrounding portions of thesilicon melt.
 21. The apparatus according to claim 17, furthercomprising a heat shield provided between the silicon single crystal andthe crucible, surrounding the silicon single crystal, in order to shieldheat dissipation from the silicon single crystal.
 22. The apparatusaccording to claim 21, further comprising a heat cover provided in theheat shield in a portion most adjacent to the silicon single crystal,surrounding the silicon single crystal.
 23. A silicon wafer manufacturedfrom silicon single crystal grown by Czochralski method, wherein abalanced region where interstitial concentration is balanced withvacancy concentration occupies at least 10% of the area of the wafer.24. A silicon wafer manufactured from silicon single crystal grown byCzochralski method, wherein an interstitial dominant region and avacancy dominant region are arranged substantially asymmetric about thecenter.
 25. A silicon wafer manufactured from silicon single crystalgrown by Czochralski method, wherein point defect concentration is thesame as or less than critical saturation concentration of vacancies thatis a minimum vacancy concentration allowing the formation of microprecipitates in heat treatment.
 26. The silicon wafer according to claim25, wherein the heat treatment comprises first heat treatment at 700 to800° C. for 5 to 7 hours and second heat treatment at 1000 to 1100° C.for 14 to 18 hours.
 27. The silicon wafer according to claim 25, whereinthe micro precipitates are formed inside the wafer at least 1 μm deepfrom the surface of the wafer, and sized 0.3 μm or less.
 28. The siliconwafer according to claim 25, wherein the point defect concentration is10¹⁰˜10¹²/cm³.
 29. The silicon wafer according to claim 25, wherein aninterstitial dominant region is a central portion of the wafer, and avacancy dominant region is in a periphery of the wafer.
 30. The siliconwafer according to claim 25, wherein the point defect concentration isuniform so that a difference between a maximum point defectconcentration (Cmax) and a minimum point defect concentration (Cmin) is10% or less of the minimum point defect concentration (Cmin) in a regionup to 90% of the radius from the center of the silicon wafer.
 31. Asilicon single crystal ingot grown by Czochralski method, wherein pointdefect concentration is 10¹⁰˜10¹²/cm³.
 32. The silicon single crystalingot according to claim 31, wherein an interstitial dominant region isa central portion of the silicon single crystal, and a vacancy dominantregion is in a periphery of the silicon single crystal.
 33. The siliconsingle crystal ingot according to claim 31, wherein the point defectconcentration is uniform so that a difference between a maximum pointdefect concentration (Cmax) and a minimum point defect concentration(Cmin) is 10% or less of the minimum point defect concentration (Cmin)in a region up to 90% of the radius from the center of the siliconsingle crystal.
 34. The silicon single crystal ingot according to claim32, wherein the interstitial dominant region and the vacancy dominantregion are substantially asymmetric about the center.